The only mistake I see is legitimizing the GP comment with a response. You don't have to justify or explain yourself, or pay any attention to this person's comments. Just be glad the behavioral problems aren't yours and have some compassion for the people who have them.

> There's no need to get sanctimonious to someone who's already down.

Absolutely. It's sickening to see, and the tone is obnoxious. Let's just move on.